I finally found a dealer who would take marked sterling and pay 80% of bullion value for it. Most coin dealers either don't want to bother if they can't resell to a collector, or will only pay half the bullion value.

If you're interested, email me and I'll give you the name. It's a dealer in the SF Bay Area that I dealt with 30 years ago and they are reliable. They also have good prices on bullion coins and bars if you are buying.